rPi Programming - Python

[last updated: 2025-03-06]
rPi home page
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• serial communication on rPi
• RS485 on rPi
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• gpio programming:
  • Setup/initialization:
    • import RPi.GPIO as gpio # "gpio" is your choice of name
    • gpio.setmode(gpio.BOARD) # this allows using board pin numbers to designate i/o
    • gpio.setmode(gpio.BCM) # this allows using gpio numbers to designate i/o
    • gpio.setup(4, gpio.OUT, initial=gpio.LOW) # "4" can be a variable
    • gpio.setup(6, gpio.IN, pull_up_down=gpio.PUD_UP)
  • Setting outputs:
    • To turn ON an output:
      gpio.output([pin# or varName], gpio.HIGH)
    • To turn it OFF:
      gpio.output([pin# or varName], gpio.LOW)
  • IRQ (callback) programming:
    • First you must define your callback/interrupt function, eg.:
      def PBpressed(channel): # "channel" is the name of the var that is returned by the function when it executes ... ???
            print("do something")
    • Then, in the code, After you've defined the function,
      gpio.add_event_detect(varName, gpio.FALLING, callback=PBpressed)

    • However:
      When I first did this on my rPi 3B+, it "failed to set event detect"
      Researching online (best guess) suggested there is a bug in this latest version of the rPIOS code ("bookworm"),
      and the workaround (that worked for me) is:
      $ sudo apt remove python3-rpi.gpio
      $ sudo apt update
      $ sudo apt install python3-rpi-lgpio

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